1. Field of the Invention
The present invention relates to a defect inspecting method for a semiconductor device.
2. Description of the Related Art
A semiconductor device is manufactured by, for example, laminating films, forming contact holes, and embedding a wiring material in contact holes. When the contact holes are formed, the wiring material cannot be embedded in the entire contact holes unless the contact holes are conductive. Therefore, a conduction inspection for the contact holes is performed when the semiconductor device is manufactured.
As a method of checking conduction after the contact holes are formed, for example, there are a voltage contrast (VC) inspection performed by using a secondary electron image and an inspection performed by using a substrate current measuring device. In both the conduction checking methods, conductive films at hole bottoms need to be earthed (needs to be conductive to a silicon wafer substrate). However, in an actual semiconductor product, the conductive films at the hole bottoms are not always earthed. This is because, in some case, insulating films are formed in layers below the conductive films at the hole bottoms.
As one of semiconductor devices in which contact holes having a large aspect ratio (a ratio of depth to a hole diameter) have to be formed, there is a semiconductor memory device in which memory cell arrays in a plurality of layers are laminated (see, for example, Japanese Patent Application Laid-Open No. 2006-155750).
However, in this semiconductor memory device, even when the conductive films at the hole bottoms are conductive to the silicon wafer substrate, most of secondary electrons collide against the sidewalls of the holes because the aspect ratio is large (the depth of the contact holes is large). Therefore, a conduction state of the contact holes cannot be inspected. In the case of an optical defect inspection, when the aspect ratio is large, a conduction state of the contact holes cannot be inspected because light does not reach the hole bottoms.
For example, in the case of a defect inspection and an optical defect inspection performed by using secondary electrons, contact holes having an aspect ratio equal to or larger than about 5 (depth equal to or larger than about 200 nanometers) cannot be inspected.